I have a question regarding checking resistance...

Background info. I'm blowing a 20A "engine sensor" fuse as soon as the keys are turned. I blow the fuse with all sensors (O2, MAF, Skipshift, reverse) plugged and unplugged. After some research, it seems that this indicates a wire from one of the sensors is grounding out somewhere. Time to track down the sensor. I'm trying to figure out how to check the resistance in each wire from the sensor to the "engine sensor" fuse.

When checking the sensors, do you put one lead (from the meter) to the sensor side of the fuse (not the 12v side) and the other to the sensor itself? Or, do you put one lead to the sensor itself and the other lead to a ground?

I'm confused on how to check. I have a bad wire somewhere.

Also, what is an acceptable resistance level? <10 Ohms?

FWIW, I tried putting one lead to the fuse and the other lead to each sensor. I found that the MAF 12v wire saw infinite resistance. I cut the connector off of the MAF pigtail and rechecked the resistance. This time the Ohm value was ~4-5 Ohms. I thought I found the problem but I'm still blowing fuses.

Ryan

 

When a fuse blows instantly like that, you are correct that the most common cause is a wire or other electrical component being grounded. "Grounded" typically means a direct connection with near ZERO resistance. This can be caused by a sensor somehow "shorting" itself and causing a near Zero resistance, or a wire's insulation is burnt/frayed/cracked and the bare conductor is touching "ground".
The reason I say "near Zero" resistance is because while a Zero resistance would cause (using Ohm's Law) an infinite current (Amps) rise, hence blowing the fuse, an VERY low resistance (say 1-2 Ohms) can still blow the fuse (using Ohm's Law) since the resulting current can be higher than the fuse rating.

A very easy way to test a short to ground is by using the ohmmeter (set to it's lowest scale, if the meter has an adjustable scale should say "x1" or something like that). Since you say you're blowing the main Sensor fuse, and you say you are blowing the fuse even after unplugging ALL the sensors....leave all sensors unplugged.
If you have access to each sensor wire leaving the fuse block, take one lead (doesn't matter since we're not concerned about polarity) and touch it to one sensor wire. Then touch the other meter lead to a very clean GROUND on the car. Most any bare metal should do. If there IS a grounded wire, the meter should read "0.00" Ohms or a VERY low Ohminc value (like 1 Ohm). Once you find this grounded wire, trace it down and find where it's grounded....OR save yourself the hassle and simply run a new sensor wire.

 

Same thing happened to me , I was blowing the engine sensor fuse and getting code PO100 and it happened to be a shorted O2 sensor. It happened a week after my header install too.

 

Don't read a wire that has voltage on it. Don't read a wire that could be connected to anything else.

Second, If you did headers it's one of the O2s grounded. If you didn't do headers it's one of the O2s grounded. Get my drift.